1. Field of the Invention
The present invention relates to rocket engines and in particular to pintle injector tips used in liquid rocket engines.
2. Background of the Prior Art
Rocket engines using more than one propellant, such as bipropellant rocket engines using two propellants, require techniques for efficiently combining the propellants. Convention techniques include the use of coaxial pintle injectors, as shown for example in U.S. Pat. Nos. 3,205,656, 3,699,772 and 4,206,594, Elverum, incorporated herein in their entirety by this reference. In such conventional pintle tips, a center or inner propellant, such as liquid oxygen or LOX, flows through a central passageway and is caused by a pintle tip to radiate outwardly through a series of apertures perpendicular to the axis of the central passageway to mix with an outer propellant, such as kerosene, flowing coaxially along the outside of the central passageway. The inner propellant is directed outward perpendicularly from the central passageway generally in the form of a set of spokes of a wheel. Various other propellants may be used and the oxidizing propellant, such as LOX, may also be caused to flow coaxially around the fuel propellant, such as kerosene.
Pintle tips are conventionally fabricated from copper or nickel and may be formed by closing the end of the central passageway, typically by fastening a separate pintle tip to a cylindrical passageway using screw threads. Conventional apertures include one or more sets of shaped passageways, slightly upstream of the closed end of the pintle tip, leading from the central passageway through a sidewall to the outer circumference of the sidewall. Such conventional pintle injector tips may utilize diverters, typically in the shape of an inverted cone mounted or formed at the end of the central passageway at the pintle tip, which are intended to cause the central propellant in the central passageway to be deflected smoothly towards the apertures for mixing outside the passageway with the outer propellant.
The downstream end or face of the pintle tip is typically adjacent the point of combustion of the combined propellants and is therefore subject to substantial heat. As a result, conventional pintle injector tips often use ablative surfaces on the downstream face of the pintle injector tip to protect the downstream face from heat damage.
Reusable rockets are very desirable designs from a cost reduction standpoint. Pintle injectors with removable pintle injector tips are desirable for use in such reusable rockets, as well as in other rocket engine and station keeping engines, because of their relatively low cost, convenience of reuse and the substantial improvement in flame or combustion stability available with coaxial pintle injector designs. Conventional coaxial pintle injector tips are somewhat limited in the convenience of their use and reuse, for example, by need for the ablative layer covering the downstream face of the tip that must be replaced after use due to erosion and charring of the ablative material. What is needed is an improved pintle tip for coaxial pintle injector engines.